Unique organ explains koala's low-pitched call
A unique vocal organ is the reason behind the koala bear's surprisingly low-pitched mating call, scientists have discovered.
The mating call of a male koala is around 20 times lower in pitch than it should be for an animal of relatively small size. In fact, scientists from the University of Sussex say it is more typical of an animal the size of an elephant.
Researchers from the university say they have managed to identify the cause - a sound-producing organ located outside the voice box, never seen in any other land-dwelling animal.
"We have discovered that koalas possess an extra pair of vocal folds that are located outside the larynx, where the oral and nasal cavities connect," explains co-author Dr Benjamin Charlton, from the university's School of Psychology.
"We also demonstrated that koalas use these additional vocal folds to produce their extremely low-pitched mating calls."
Dr Charlton describes the marsupial's call as being similar to a donkey's braying, with a continuous series of sounds as the animal inhales and exhales.
According to scientists, the dimensions of the laryngeal vocal folds usually restrict the lowest pitch that the animal can produce, meaning smaller species generally give higher-pitched calls than larger animals.
Research from the team in Sussex, titled "Koalas use a novel vocal organ to produce unusually low-pitched mating calls", suggests that koalas have overcome this constraint by developing vocal folds in a new, highly unusual location.
Co-author of the research, Dr David Reby, adds: "To our knowledge, the only other example of a specialised sound-producing organ in mammals that is independent of the larynx are the phonic lips that toothed whales use to generate echolocation clicks."
Data gathered in this study, which was published in Current Biology on December 2, represents the first evidence of an organ dedicated to sound production in a mammal, other than the larynx.
Dr Charlton and his colleagues now plan to look more closely at other mammals, to determine whether this vocal organ really is unique to koalas.
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